In conveyor systems for conveying and distributing articles, a series of conveyed articles are typically transported along moving conveying surfaces. Conventional conveyor systems often include one or more sortation conveyors which divert selected articles from a primary conveying path onto one or more secondary conveying paths.
Sortation conveyors often employ pusher elements which are mounted relative to the conveying surface. Often, the pusher elements are mounted such that they may be selectively moved across the conveying surface in order to eject an article from the primary conveying path and onto a secondary conveying path. One particular sortation conveyor of this type is referred to as a “shoe sorter,” wherein the pusher elements are termed “divert shoes.”
In a typical conventional shoe sorter, the primary conveying surface is provided by multiple transverse tubes (rollers) or slats which form the conveying surface. Multiple pusher elements are part of or supported by the conveying surface and are guided in a set position along the length of the sorter during normal forward operation. The pusher elements can take on many forms such as belted slats, pins, and molded blocks. Historically, the most prevalent design is referred to as a shoe, although other designs are possible. Here after the term shoe and pusher element shall be used to include all conventional shoes, as well as other diverting elements such as but not limited to slats, belts, rollers, etc. To direct an article from the primary conveying path onto a secondary conveying path, a switch mechanism can be engaged to cause an assigned set of pusher elements to slide across the conveying surface in a diagonal direction. The diverted pusher elements engage and divert the article to the secondary conveying path. Such shoe sorters often use guide tracks or guide surfaces which direct the assigned set of shoes laterally across the conveying surface, while shoes which are not assigned continue to travel along the conveying surface in their set position
In conventional sortation conveyors, a control system ensures that the appropriate set of pusher elements is assigned to each article, and that the assigned pusher elements are directed across the primary conveying surface at the proper time (i.e., when an article needs to be directed or pushed to a secondary conveying path rather than remain on the primary conveying path). Sorter throughput depends on a variety of factors, particularly the speed of the conveying surface and the size of the gap between adjacent articles being sorted. Higher throughput means that more articles can be handled faster and that handling costs can be reduced (e.g., because fewer distribution facilities may be required, less man-hours may be required to operate machinery, etc.). If the size of the gap is small, it can be difficult for the control system to not only assign the proper set of pusher elements, but also ensure that the assigned set of pusher elements are diverted across the conveying surface at the proper time. However, increasing the speed can introduce other problems such as increased maintenance and decreased controllability. Accordingly, it is desired to provide methods and systems that increase conveyor throughput for a given conveyor speed, while maintaining adequate sortation accuracy and timing.